Subterranean drilling systems that employ downhole drilling motors are commonly used for drilling boreholes in the earth for oil and gas exploration. Subterranean drilling systems typically include a housing enclosing a downhole drilling motor operably connected to an output shaft. One or more thrust-bearing apparatuses may also be operably coupled to the downhole drilling motor for carrying thrust loads generated during drilling operations.
Each thrust-bearing apparatus may include a stator that does not rotate and a rotor that is attached to the output shaft and rotates with the output shaft. The stator and rotor may each include a plurality of superhard bearing elements or inserts. Each superhard bearing element may be fabricated from a polycrystalline diamond compact (“PDC”) that provides a diamond bearing surface that bears against other diamond bearing surfaces during use.
In a conventional PDC thrust-bearing apparatus, a thrust-bearing assembly can include a steel support ring that may be configured to accept a number of superhard bearing elements. The superhard bearing elements may be made from a polycrystalline diamond (“PCD”) layer formed on a cemented tungsten carbide substrate. The superhard bearing elements may then be brazed into the support ring using a brazing process.
Brazing the superhard bearing elements into the support ring involves high temperatures that can damage (e.g., graphitize) the polycrystalline diamond of the superhard bearing elements and can also cause the bearing ring to warp. In addition, the support ring and superhard bearing elements should be very clean in order to achieve a brazed joint between the support ring and superhard bearing elements with sufficient strength to withstand the forces applied to the superhard bearing elements during drilling operations. Despite best efforts, brazed joints may, nonetheless, fail during use or testing.
Therefore, manufacturers and users of bearing apparatuses continue to seek improved bearing apparatus designs and manufacturing techniques.